The invention relates generally to signal processing, and more particularly to systems and methods for reducing the noise floor in digital X-ray imaging systems.
A number of radiological imaging systems of various designs are known and are presently in use. Certain of these systems are based upon generation of X-rays that are directed toward a subject of interest. The X-rays traverse the subject and, in digital imaging system, impact a digital detector. Such X-ray systems use digital circuitry for detecting the X-rays, which are attenuated, scattered or absorbed by the intervening structures of the subject. In medical diagnostic contexts, for example, such systems may be used to visualize internal tissues and diagnose patient ailments. In other contexts, parts, baggage, parcels, and other subjects may be imaged to assess their contents and for other purposes.
Basic radiographic X-ray systems may be designed for generating projection images only. Such projection images may be presented as a well-known reverse image, although the image data itself is subject to various presentations. In addition to radiographic X-ray systems, fluoroscopy systems, computed tomography systems, and tomosynthesis (CT) systems that are based on similar X-ray radiation generation and detection are also used to generate images. In fluoroscopy systems, for example, a low dose X-ray signal may be used to generate a real-time moving image.
Quantum and electronic noise in the measurement system may tend to cause various artifacts in the radiological data collected in any one of the foregoing types of systems. Such artifacts are not only distracting, but may impair effective use of the images, such as for diagnosis in a medical context. In particular, such artifacts may make small or more detailed features that would otherwise be visible in the images, difficult to detect and discern. Therefore, reducing the noise floor may result in improved image quality and also enable lower dose protocols.
In applications such as mammography and radiography, the X-ray source energy is high, and the gain of the receiving electronics is relatively low. This allows the receiver to generate an image with a high dynamic range. In such systems, the noise floor is dominated by intrinsic X-ray quantum noise, and the noise generated by the electronics is not as important. In applications such as fluoroscopy systems, the X-ray source energy is low and the gain of the receiver circuitry is relatively high. This reduces the overall X-ray exposure to the patient, while still producing a suitable image. In these types of systems, the noise floor is dominated by the receive circuitry.
Existing techniques for reducing the noise floor in a variety of applications are typically tailored to adapt to a given X-ray application, based on the strength of the X-ray source signal. Accordingly, multiple image processing platforms may have to be developed, each with a different noise reduction technique depending on the X-ray application.
It would be advantageous, therefore, to provide improved techniques for reducing noise in radiological image data that may be used for a wide range of signal levels, thus allowing a single image processing platform to be used with a wide range of X-ray applications.